1. Field of the Invention
This invention relates to certain activator-stabilizer precursors for use in photographic materials for processing with heat. More specifically, this invention relates to such compounds having an acid portion and a base portion which comprise certain acylhydrazines which release a base moiety upon being heated to a temperature above about 130.degree. C. One aspect of the invention relates to a heat developable and heat stabilizable photographic element comprising the described activator-stabilizer precursor. Another aspect relates to certain photographic compositions for processing with heat containing these compounds. A further aspect relates to a thermosensitive photographic processing composition containing the described activator-stabilizer precursors.
2. Description of the State of the Art
Photographic elements that are heat processable are well known. That is, a photographic element is known wherein a latent image can be developed after imagewise exposure by merely heating the element. Typically, such elements can contain photosensitive silver halide, a silver halide developing agent, and an activator precursor with, typically, a stabilizer precursor to provide a developed and stabilized image. Development of the latent image and stabilization occur substantially simultaneously as the result of two competing reactions. It is necessary that the activator precursors and stabilizer precursors or activator-stabilizer precursors in such heat processable photographic elements be such as to permit the respective reactions to take place without adversely affecting the desired sensitometric properties of the photographic element.
It is known to incorporate activator-stabilizer precursors into heat processable photographic materials. Typical activator-stabilizer precursors are described in, for instance, U.S. Pat. No. 4,012,260 of Dickerson and Merkel. An example of such an activator-stabilizer precursor is a 2-amino-2-thiazolium carboxylate. Upon heating the photographic material containing such an activator-stabilizer precursor and a developing agent, an agent is released that is capable of activating the developing agent to enable latent image development and substantially simultaneously permit stabilization of the resulting developed image in the photographic material. Another example of an activator-stabilizer precursor is described in U.S. Pat. No. 4,060,420 of Merkel and Ling. This activator-stabilizer precursor is one which contains a base moiety and an acid moiety in which the acid moiety is an .alpha.-sulfonylacetate. A further example of an activator-stabilizer precursor in a heat processable photographic element is described in U.S. Pat. No. 4,088,496 of Merkel. This relates to an activator-stabilizer precursor containing an acid moiety and a base moiety in which the acid moiety is a 2-carboxycarboxamide.
Certain problems have been encountered with the described activator-stabilizer precursors. The byproducts of the 2-amino-2-thiazolium carboxylates formed by decarboxylation are undesirably volatile at processing temperatures in the heat processable photographic element. The .alpha.-sulfonylacetate activator-stabilizer precursors provide activation and stabilization without significant volatile byproducts of decarboxylation; however, it has been noted that compounds containing the .alpha.-sulfonylacetate produce what is described in the photographic art as "pinholes" in the photographic element upon processing. "Pinholes" as described herein mean small areas of low density in the photographic material that can be readily observed visually through a 10X magnifier. The "pinholes" are most readily apparent in the maximum density areas of the developed photographic material. This property is particularly disadvantageous for microimaging purposes. The described 2-carboxycarboxamide activator-stabilizer precursors are useful to help avoid the described disadvantages. However, the photographic elements containing the 2-carboxycarboxamides produce an undesired degree of visible crystal formation in the processed photographic element. None of the described activator-stabilizer precursors have provided answers to other of the described problems as well as a suitable answer to this crystal formation problem. A continuing need has existed to find a suitable answer to the crystal formation problem, especially for photographic elements designed for microimaging.
Photographic materials containing a variety of hydrazine and hydrazide compounds are also known. Hydrazides have in certain instances been useful as activators in certain heat processable photographic materials. Such hydrazide activators are described in, for instance, U.S. Pat. No. 3,506,444 of Haist and Burness. In addition, hydrazine and hydrazides have been in some instances effective reducing agents in certain heat processable photographic materials. Such hydrazine and hydrazide reducing agents are described in, for example, U.S. Pat. No. 3,667,958 of Evans. The described hydrazine and hydrazide reducing agents do not contain heat releasable acid groups; this enables them to produce both activation and stabilization of an image in a photographic material that is designed to be heat processable. Also, hydrazide developing agents have been described in U.S. Pat. No. 3,782,949 of Olivares, Bean and Haist. The hydrazine developing agents, however, have no function as activator-stabilizer precursors in the photographic materials. In addition, the described hydrazinehydrazide reducing agents have provided no suitable answer to the problem of avoiding visible crystal formation in a heat processed photographic element as described.
There has been a continuing need for improved activator-stabilizer precursors that (a) do not produce undesirable volatile byproducts, (b) reduce the number of undesired "pinholes" and (c) help provide essential freedom from visible crystal formation in a heat developable and heat stabilizable photographic element as described herein.